(1) Field of the Invention
The present invention concerns a system and a method of analysis of an object, or of a sample, by determining its depolarising or dichroic character.
It is considered that an object has a dichroic character if it exhibits loss anisotropy.
Polarimetric imaging finds applications in a large number of fields, and in particular in the field of biomedical imaging. Polarimetric imaging is based on an analysis of the modification of the state of polarisation of a light beam when it is back-scattered or forward-scattered by an object, or a sample, to be analysed.
In dermatology for example, polarimetric images of the skin may allow detecting melanomas or lupus. Polarimetric imaging also allows detecting irradiation of the skin, much before the clinical signs of such irradiation appear. Another application is support to the diagnosis of pathologies on biological tissues for detecting cancer of the uterus or for analysing liver cirrhosis progress.
(2) Description of Related Art
All these techniques are based on perfect knowledge of the polarimetric state of the light beam projected onto the object or sample to be analysed and on a precise measurement of the state of polarisation of the light beam forward-scattered or back-scattered by the object or sample to be analysed. Such an approach is not very compatible with the use of an optical guide, such as an optical fibre, for transferring the effective transmission and/or effective reception of the light beam. This constraint considerably limits the fields of application of polarimetric imaging, in particular with regard to in situ and/or in vivo medical diagnoses.
This is because an optical fibre always exhibits residual birefringencies that change in particular according to the curvatures of the fibre, which is for example the case in endoscopic imaging, where the fibre undergoes mechanical compression and torsion stresses that are in principle unpredictable. These residual birefringencies cause variations that are not deterministic of the polarimetric state of the light beam during propagation thereof in the optical fibre.
So as to allow transfer by optical fibre, the patent application published under the reference FR 2 941 047 A1 proposes a mechanism for determining information on polarisation of a measurement point of a sample by using means for rotating the polarisation disposed at the end of the optical fibre on the same side as the sample to be analysed. The birefringent or depolarising character of the sample, at a given point, is then obtained by statistical analysis of shots of various random polarisation states at the entry to the fibre. However this proposition requires an acquisition time for the measurements that is incompatible with the real-time imaging and endoscopic imaging requirements.